Hours Calculator
Time Duration Tool
Use the calculators below to find the number of hours and minutes between two times. For a full time card, please use the Time Card Calculator.
Understanding Time and Hours
An hour is most commonly defined as a period of time equal to 60 minutes, where a minute is equal to 60 seconds, and a second has a rigorous scientific definition. There are also 24 hours in a day. Most people read time using either a 12-hour clock or a 24-hour clock.
12-Hour Clock
A 12-hour clock uses the numbers 1-12. On digital clocks and watches, "AM" stands for ante meridiem, meaning "before midday," while "PM" stands for post meridiem, or "after noon." By convention, 12 AM denotes midnight, while 12 PM denotes noon.
24-Hour Clock
A 24-hour clock uses the numbers 0-23, where 00:00 indicates midnight. It's an international standard used to avoid ambiguity. The hours from 0-11 denote AM hours, and 12-23 denote PM hours. It is often referred to as military time.
Hours in Different Time Periods
| Description | Hours |
|---|---|
| Hours in a day | 24 |
| Hours in a week | 168 |
| Hours in a month |
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| Hours in a year |
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| Hours in a decade |
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| Hours in a century |
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Key Takeaways
- 12-Hour vs 24-Hour: AM/PM markers are only used in 12-hour systems; 24-hour systems (military time) use 00:00 to 23:59 to avoid ambiguity.
- Decimal Conversion: To convert minutes to decimals, divide by 60 (e.g., 30 mins = 0.5 hours). This is crucial for payroll and billing.
- Cross-Day Calculation: When calculating between dates, always account for leap years and daylight saving time for high-precision needs.
- Standard Units: One standard week contains exactly 168 hours, based on the conventional 24-hour day structure.